1. Field of the Invention
The present invention relates to nonreciprocal circuit elements and methods of manufacturing a nonreciprocal circuit element. Particularly, the present invention relates to a nonreciprocal circuit element that is small in size, that exhibits high performance, and that is suitable for mass production, and to a manufacturing method thereof.
2. Description of the Related Art
Lumped-constant isolators, which are a type of nonreciprocal circuit element, are high-frequency components that allow signals to be transmitted in a direction of transmission without a loss while inhibiting transmission of signals in the opposite direction, and are used in transmission circuits of mobile communication devices such as cellular phones. Recently, as the sizes of cellular phones become smaller, a demand exists for further miniaturization of isolators used in cellular phones.
As nonreciprocal circuit elements that are similar to isolators, circulators are known. Techniques for reducing the sizes of circulators and improving performance thereof are disclosed in FIG. 10 of Japanese Unexamined Patent Application Publication No. 6-338707. FIG. 10 of Japanese Unexamined Patent Application Publication No. 6-338707 discloses a circulator in which conductors are embedded in a YIG lamination and the conductors are connected to a magnetic rotor via through holes or the like in order to reduce size and improve performance.
The magnetic rotor mentioned above is manufactured by coating green sheets composed of YIG powder, binder, and flux with silver paste or the like by printing or the like, and sintering the green sheets. However, when silver paste or the like is used, sintering temperature must be kept low. This has lead to insufficient sintering and failure to obtain a YIG magnetic component having satisfactory characteristics. Thus, it has been difficult to improve performance of circulators.
Furthermore, the magnetic rotor manufactured has a polygonal shape. Thus, when the magnetic rotor is contained in a substantially rectangular-parallelepiped case, a useless space is formed between the magnetic rotor and the case, inhibiting miniaturization of circulators.